As well known by those skilled in the art, chromatographic systems rely on the use of valves to allow reproducible sample introduction and various column switching schemes.
Diaphragm valves of various designs are known in the art for chromatography applications. Such diaphragm valves have been used in many commercially available gas chromatographs. They are apt to be integrated more easily in a gas chromatograph due to their physical size and since the actuator is embedded in the valve itself. These characteristics make them attractive for gas chromatograph manufacturers.
Referring to FIG. 1 (PRIOR ART), there is shown an example of a typical diaphragm-sealed valve as known in the art. The valve 1 is provided with a top block 2 having an interface 4 and a plurality of ports 6. Each one of the ports 6 opens at the interface 4 and has a thread passage 8 to connect various analytical fitting and tubing (not shown). At the bottom of the thread passage 8, there is a conduit 10 extending in the top block 2 and opening into the ports 6 at the interface 4. The ports 6 are arranged along a line, such as, for example, a circular line, on the interface 4 of the top block 2. The interface 4 is advantageously flat and polished to minimize leaks between ports 6 and from the ambient atmosphere. The valve 1 is also provided with a bottom block 12 and a diaphragm 14, which is generally made of material such as polyimide, Teflon™ (polytetrafluoroethylene) or other polymers. The diaphragm 14 is positioned between the top block interface 4 and the bottom block 12, and has a recess 18 therein extending along a line formed by the ports 6 and biased away from the interface 4 of the top block 2. The recess 18 in the diaphragm 14 sits in a matching recess 20 made in the bottom block 12, thereby allowing some clearance for fluid circulation between adjacent ports 6.
The valve 1 is also provided with a plurality of plungers 16 mounted in the bottom block 12, each one of the plungers 16 being respectively arranged to compress the diaphragm 14 against the top block 2 at a position located between two of the ports 6. Preferably and as illustrated, in the case of a six port valve, when the valve is at rest, three plungers 16 are up while the other three are down. When the plungers 16 are up, they compress the diaphragm 14 against the top block 2 and close the conduits made by the diaphragm recess 18, so that fluid circulation is blocked. The bottom block 12 keeps the plungers 16 and the actuation system moving the plungers 16 between the up and down configurations, in position.
It is common to designate a portion of the plungers 16 as “normally open” and another portion of the plungers 16 as “normally closed”. A normally open plunger 16 is biased downwards, i.e. away from the diaphragm 14, and therefore normally allows fluid circulation between the two adjacent ports 6. A normally closed plunger 16 is biased upwards, i.e. towards the diaphragm 14, and therefore blocks fluid circulation between the two adjacent ports 6. The valve 1 may be actuated in order to alter the positions of the plungers 16, for example by sliding upwards and downwards the normally open and normally closed plungers 16, respectively.
In many cases a gas sampled by the diaphragm-sealed valve or a carrier gas used to carry the sample gas can be a corrosive, a toxic, an unstable and/or a reactive gas. For example and without being limitative, the gas may comprise hydrogen fluoride, silane, phosphine, ammonia, chlorine, boron trichloride, nitrogen trifluoride, fluorine, bromine, hydrogen, arsine, phosphine or the like. When such gases are used with known gas chromatograph diaphragm valve, the gases are isolated from the actuation system of the valve, and the ambient air by the diaphragm.
However, over time, the diaphragm could be punctured, for example due to material aging, over-pressure operation, high velocity abrasion, sample contamination and/or by-products generation. When the diaphragm is punctured, undesirable leak of the sample and/or the carrier gas into the actuating mechanism of the actuation system of the valve, or release of the gas into the ambient air may occur. Moreover, using known valve, such leaks are difficult to detect promptly in order to initiate desirable actions.
Depending of the nature of the sample and/or the carrier gas, this could result in undesirable damage to the valve, the instrument where the valve is installed or to auxiliary equipment used to control the valve. Those skilled in the art know to take great care when dealing with such gases, and a careful control of the environment in which they are used is performed.
It is known to use o-rings between the components in order to reduce the potential flow of gas between components of the valve, subsequently to a leak through the diaphragm. However, the use of o-rings often proves to be unsatisfying when the leaked sampling and/or carrier gas is a corrosive, a toxic, an unstable and/or a reactive gas.
In view of the above, there is a need for an improved valve, chromatographic system using the same and a method of operation thereof which, would be able to overcome or at least minimize some of the above-discussed prior art concerns.